This invention relates to contacts and interconnects for semiconductor integrated circuit devices, and more particularly to methods of manufacture of MOS VLSI devices employing metal contacts made through apertures in an insulator coating.
In the manufacture of MOS VLSI devices, for example dynamic RAMs as disclosed in U.S. Pat. Nos. 4,055,444 and 4,388,121, issued to G. R. Mohan Rao, assigned to Texas Instruments, it has been the practice to employ a phosphosilicate glass as an insulating coating, and to make contacts to the silicon or other layers beneath the insulator by etching holes in the insulator then flowing the insulator by heating ("densifying") to slope the sidewalls. Thus, the deposited metal would cover the sloped walls with no discontinuities. However, in the manufacture of devices of extremely high component density, as needed for DRAMs of the 1-Megabit size, for example, it is necessary to make the sidewalls of the contact holes vertical instead of sloped, to save space. This can cause voids in the contact because the contact hole is not filled with metal by conventional sputtering or evaporation; i.e., the step coverage is poor and cracks can develop at the point where the metal goes over the edge. In order to avoid the step coverage problem, it has been proposed that CVD or chemical vapor deposited metal be used since this deposition method is isotropic and covers all surfaces equally, but the quality of CVD metal is not good enough to be the primary conductor in the metallization system.
Another problem is that as the minimum dimensions are reduced to the one or two micron range then the succeptability to electromigration is increased since there is much less metal in the interconnect and it can be destroyed more easily; electromigration results from high current densities in the small conductors, and contact with phosphorus-containing material such as the phosphosilicate glass used as the insulator layer causes corrosion of the metal.
It is the principal object of this invention to provide an improved method of making contacts to semiconductor integrated circuit devices, particularly VLSI devices having very small dimensions. Another object is to provide contact methods useful for high density integrated circuit devices, wherein contact holes in insulator layers are formed with vertical sidewalls. A further object is to provide a contact method which does not require a high temperature operation to slope the sidewalls of a contact hole. Still another object is to minimize the detrimental effects of electromigration and chemical corrosion.